1. Field of the Invention
The present invention relates to a battery module.
2. Description of the Related Art
A rechargeable battery can be repeatedly charged and discharged unlike a primary battery which cannot be recharged. A low-capacity rechargeable battery is used for small electronic devices which are portable, such as mobile phones, laptop computer, and camcorders. A large-capacity battery is used as a power source for driving motors, such as for hybrid electric vehicles.
In recent years, a high-power rechargeable battery using a non-aqueous electrolyte having a high energy density is being developed. The high-power rechargeable battery includes a battery module in which a plurality of rechargeable batteries is coupled in series so that the high-power rechargeable battery can be used to drive the motors of devices requiring high power, such as electric vehicles.
Further, a battery module generally includes a plurality of rechargeable batteries coupled in series (each hereinafter referred to as a ‘unit battery,’ for convenience of description), and each of the rechargeable batteries may have a cylindrical or square shape.
Each of the unit batteries includes a casing, having an electrode assembly placed with a separator between a positive electrode and a negative electrode, and space where the electrode assembly is placed, a cap assembly configured to close and seal the casing, and electrode terminals electrically connected to the electrode assembly and configured to externally protrude through the cap assembly.
Furthermore, the positive and negative terminals of each of the unit batteries are arranged to cross the positive and negative terminals of a neighbor unit battery so that the unit batteries can be coupled to each other in series. A connection member is inserted between the positive terminal of a unit battery on one side and the negative terminal of a neighbor unit battery, and nuts placed over the connection member are engaged with the positive terminal and the negative terminal. Accordingly, the unit batteries are coupled in series via the connection member.
To this end, holes are formed in the connection member into which the positive terminal and the negative terminal are inserted, and outer circumferential surfaces of the positive and negative terminals are processed to have a screw shape for engagement with the nuts.
However, high contact resistance is generated at a surface where the nuts come into contact with the connection member.
This phenomenon is caused by a small contact area between the nuts and the connection member. That is, although the connection member and the nuts are processed to have a smooth surface externally, the surface is formed to have uneven portions because of limits to processing. Accordingly, when the contact portion of the nuts and the connection member is checked microscopically in the state where the nuts are engaged with the positive terminal and the negative terminal, the contact portion is a small area.
The conventional battery module produces low output power because of increased contact resistance at the contact portion of the unit battery, resulting in resistance heat generated at the contact portion. Moreover, the nuts used for fastening may become loose because of external vibration. In this case, the contact portion may have even greater contact resistance, resulting in even more heat generated.
Battery module designers have proposed welding the connection member to the terminals. However, in this case, it is difficult to separate the unit battery from the battery module.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.